It is known, as published in "Journal of Materials Science" 20 (1985), page 3697, in "Ceramics International" 15 (1989), page 271 or in "Journal of Material Science" 16(1981), 2997, that at high temperatures, reactions of the type EQU AlN+ZrO.sub.2 .fwdarw.Al.sub.2 O.sub.3 +ZrN+N.sub.2 + other crystalline phases (1) EQU AlN+TiO.sub.2 .fwdarw.Al.sub.2 O.sub.3 +TiN+N.sub.2 + other crystalline phases (2)
may take place. In these above reactions, by the term "other crystalline phases" suboxides or oxynitrides, in different valency state of the corresponding metals, are intended.
It is also known that materials of the type of metal nitrides, such as for instance zirconium or titanium nitride, are good electroconductive materials and have hardness and tribologic characteristics such to be used in ceramic composite materials useful as anti-wear materials, for instance in coatings or inserts for cutting tools.
To this purpose powders of metal nitrides and alumina having suitable granulometries, can be mixed intimately and sintered at high temperature and under pressure or can be deposited on the material surfaces by techniques such as "physical vapor deposition".
On the contrary, ceramic compositions obtained by reactions (1) and (2) are not suitable for practical uses in that they have reduced mechanical and electrical characteristics and low stability and/or controllability.
The applicants have now found that if reactions of the type (1) and (2) are carried out under suitable process conditions, it is possible to obtain compositions, essentially consisting of alumina and metal nitrides, with high density and exhibiting homogeneous and isotropic scattering of components.
The thus obtained compositions are suitable for practical applications in that they are endowed with mechanical and tribologic properties higher than those of analogous compositions obtained by the above mentioned conventional sintering processes and can be worked by spark erosion techniques.